investigating interactions with mixed models

I'm investigating a number of dependent variables using mixed models, e.g.

data.lmer45 = lmer(ampStopB ~ (type + stress + MorD)^3 + (1|speaker) + 
(1|word), data=data)

The p-values for some of the 2-way and 3-way interactions are significant 
at a 0.05 level and I have been trying to find out how to understand the 
exact nature of the interactions. Does anyone know if it is possible to run 
post-hoc tests on mixed model (lmer) objects? I have read about TukeyHSD 
but it seems that this can only be run on anova (aov) objects.

Any suggestions would be gratefully appreciated!

Rachel Baker

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PhD student                
Dept of Linguistics        
Sidgwick Avenue
University of Cambridge              
Cambridge